This research is directed at understanding aging changes in the anatomy and synaptology of the luteinizing hormone-releasing hormone (LHRH) system. The animal model is the rat as this is the species on which most aging study has been done. The specific aims of the proposed studies are to investigate the ultrastructure of LHRH neurons and their dendrites in the preoptic area (POA) and their axons and terminal fields in the medial basal hypothalamus (MBH) and median eminence (ME) in the male rat, using adult (2-4 mos), middle aged (10-12 mos) and old (22-24 mos) animals. Age changes will be observed in the relationship of these neurons and their processes to their affective milieu. Four modulators of LHRH release which are known to be affected by aging have been chosen for these studies: norepinephrine, neurotensin, beta-endorphin and serotonin. Morphometric analyses will be made of immunocytochemically identified elements including perikaryal components (nucleus, nucleoli, rough endoplasmic reticulum, Golgi apparatus), dendrites, axon terminals, and pre- and post-synaptic characteristics. The proposed electron microscopic, immunocytochemical studies fall into three categories: 1. Aging changes in the ultrastructure and synaptology of LHRH neurons in the POA. a. Morphometric analysis and synaptology of LHRH neurons b. Analysis of noradrenergic input to LHRH neurons c. Study of interrelation between neurotensin and LHRH neurons 2. Aging changes in ultrastructure and input to LHRH neurons in MBH. a. Morphometric study of synaptology of LHRH processes and their relationship to each other and their affective milieu b. Analysis of LHRH processes and beta-endorphin neurons c. Analysis of serotoninergic input to LHRH processes 3. Aging changes in the ultrastructure of LHRH axons and their proximity to the fenestrated capillaries of the median eminence.